Experience With Non-Vanos BMW M62 Engine Requested - Misfire Issue

[ccconant]

Hi guys.

I don't mean to post unrelated vehicle crap here, but everyone on this site is so much more understanding than other BMW flame-"fests".

Anyway, does anyone have extensive experience with the M62 (as in 540, 740, 840, X5 4.4, Range Rover - if you're unlucky, Morgan Aero 8 - if you're lucky)? I have an extremely annoying misfire issue I'm trying to track down and I haven't had much luck for about a month now.

If anyone does have knowledge or experience, I'll post or PM details. If not, sorry for bringing it up here, and keep rocking the M54 :).

[kayger12]

Post up some details and I'm sure we can at least bounce some ideas around for you.

Symptoms, codes, and what you've tried so far?

[ccconant]

Here's my summary:


Good evening folks.

I've been having a problem for about a month now with my '97 540i 6-speed (non-VANOS, just hit 114k miles this week). Above ~4000 RPM at anything near full throttle, I get a very hard and noticeable misfire, accompanied by a flashing CEL (obviously), and codes 0300 (random misfire), 0305 (cyl. 5 misfire), and 0308 (cyl 8 misfire).

I've also been getting noticeably poorer fuel economy, even when driving conservatively as I usually do. I rarely exceed 3000 RPM in normal driving, so the misfire is mainly an annoying niggle that won't give me full power when I want it. Now I'm forced to drive like a granny.

Modifications from stock:

Dinan CAI
Dinan "Stage 2" Software
Rear muffler/resonator delete
None of these should really make any difference with my problem.

I had replaced the CCV a few months prior, so I doubt it's related (i.e. improbable, but not impossible). There was a decent amount of oil buildup in the plug wells, but everything was cleaned thoroughly after the fact, and as you will see later this is probably not the cause.

Hmm, so what causes misfiring? Lean misfire? Too much air, MAF issues, not enough fuel, O2 sensors, ignition issues, etc. I started by cleaning the MAF, throttle body and IAC valve, and checking all connections, grounds, vacuum lines, etc. I changed the plugs (replaced with OEM-recommended NGK BKR6EK).

I tested all the coil packs AND boots for resistance and they all matched and were within specs. Just for fun, I swapped the coil packs from cylinders 5 and 8 with those from cylinders 1 and 2. Absolutely zero change, except now I was getting code 0306 (cyl. 6 misfire) instead of 5.

Okay, so the misfiring is all on one bank (passenger side). What causes only one bank to misfire? It's not anything before the throttle body, for sure (not much there, and that would most likely cause both banks to misfire).

Possibilities:

Fuel injectors? Maybe, probably not. The misfire jumped from cylinder 5 to 6 without me moving anything fuel-related.

Intake manifold gaskets? Maybe, but why would it be only one side? Insight here?

Fuel filter? Probably not, that would be both banks lean misfiring and the fuel volume flow (hidden OBC #4.2) would probably be lower than normal as well. It isn't.

O2 sensors? Definite possibility. Haven't had the chance to test for that yet.

:( And now the dreaded option: clogged cat for bank #2? How would this jack up the O2 sensor readings? Is this a stupid option or am I being reasonable?

I'd like to systematically go through more inexpensive options before I go replacing (or yanking) cats. Any brilliant ideas or anything I've completely overlooked? I'd appreciate any help. Thanks guys (and a the few girls).

So far, public opinion (and my own) is leaning toward a clogged cat on bank 2. At 114k miles, this is a completely feasible option. However, being that it is the worst and most expensive option, I'd like to wait a bit and see if any other brilliant ideas crop up :).

Thanks for the help; I appreciate it!